Polysiloxane fluids may be prepared using acid clays as catalysts to effect the necessary breaking and reforming of siloxane bonds to attain linear fluid polymers from mixtures of cyclic organopolysiloxanes, endblocking hexalkyldisiloxane and any added linear polysiloxane oligomers. For example, U.S. Pat. No. 4,622,412, discloses the use of acid clay catalyst (Filtrol 13, available from Filtrol Corporation) to form a mercaptofunctional polysiloxane fluid from lower molecular weight siloxane precursors. The use of acid clay catalysts may also be employed to breakdown or depolymerize polysiloxanes--leading to removal of volatile lower molecular weight products. U.S. Pat. No. 3,714,213 (Miller) for example, teaches the use of acid treated clay or synthetic alumina silicate as cracking catalysts to convert methyl hydrogen polysiloxane fluid to volatile methyl hydrogen cyclic polysiloxanes.
When silicone fluids are used as release agents in electrostatic copying machines to effect release of toner treated paper from the heated fuser roll, substantial contamination of the fluid by acidic kaolin clay is incurred. According to U.S. Pat. Nos. 4,588,771, 4,612,055 and 4,644,074 this contamination is caused by the presence of kaolin clay in the paper, which collects in the copying machine sump along with excess release agent. When the sump contents are reused, the combination of acidic kaolin clay and the high temperature of the fuser roll results in breakdown to lower molecular weight silicone products. The content of kaolin clay varies in paper stocks, along with the degree of dusting of paper fines, giving variations in silicone release agent performance that are related to paper stock. Various makes and models of copying machines also employ different fuser roll temperatures, with higher temperatures exacerbating the degrading effects of kaolin clay contamination of silicone fluid release agents.
Degradation of silicone release agents leads to a loss of copying machine efficiency as evidenced by poor release, buildup of residue on fuser rolls and evolution of siloxane volatiles, which can inhibit proper functioning of electrical switch contacts in the machines--due to the insulating properties of the silicone degradation products.
U.S. Pat. Nos. 4,588,771, 4,612,055, and 4,644,074 disclose the use of an amine containing compound as an inhibitor to degradation in kaolin clay containing organopolysiloxanes, or thiofunctional polysiloxane fluids, or blends of organopolysiloxane fluids with thiofunctional polysiloxane fluids.
Despite the cited stability improvements of these silicones (modified by the addition of amine compound) in the presence of kaolin clay and heat, a need still exists for improved products that do not require potentially hazardous or corrosive amine compounds for stability enhancement.
The organic amine compounds disclosed in U.S. Pat. Nos. 4,588,771, 4,612,055 and 4,644,074 are, in some instances, toxic materials that might present safety problems when used in copier machine release agents. 4,4'- bis (alpha-methylbenzyl) diphenyl amine (BDPA), disclosed in example 1 of each of the above three patents, is a member of the diarylamine family of amine compounds.
According to the Encyclopedia of Chemical Technology by Kirk-Othmer, Third Edition, Vol. 2, Pg. 335, Anthramine (a higher diarylamine) has been found to cause tumors in mice and rats. This same reference book, on page 334, states that both DuPont and BF Goodrich ceased production of another diarylamine (N-phenyl-B-naphthylamine) "because it metabolizes in the body to produce small amounts of 2-naphthylamine, a known carcinogen."
The Hazardous Chemicals Desk Reference by Sax and Lewis (Published by VanNostrand Reinhold Company - Copyright 1987) lists diphenylamine as an experimental teratogen and a poison by ingestion on page 449.
This same reference book, on page 184, states: "Aromatic Amines contain one or more rings of unsaturated or cyclic hydrocarbon, such as benzene. There are a vast number of such amines. Many of these aromatic amines are recognized as carcinogenic to the human bladder, ureter, and renal pelvis, and carcinogenic to the intestines, lung, liver and prostrate."
This same reference also states, on page 145, that amines, in general, range from poisons to slightly toxic compounds. Many are considered to be skin irritants and some are sensitizers.
In addition to the potential health hazards of amine compounds, the corrosive nature of many amines further demonstrates the need for an improved additive for silicone release agents used in copying machines.
U.S. Pat. No. 3,819,563 discusses negative effects of amines evolved from room temperature vulcanizing silicone compositions stating that: "Amines, along with acids and oximes, generate poisonous or corrosive gases which may corrode metallic substrates."
U.S. Pat. No. 4,318,939 discusses corrosiveness of amines, especially when used in electronic devices. Column 4, lines 50-57 states: "Furthermore, amines are corrosive to certain metals such as aluminum which is often present in electronic devices. Hence, when the formulation is employed as an encapsulant for electronic devices, the use of amine must be avoided."
Therefore, it is the object of this invention to provide amine compound-free stabilized siloxane fluids. Another object is to provide a process for stabilizing organopolysiloxane fluids, thiofunctional polysiloxane fluids or blends of organopolysiloxane fluids and thiofunctional polysiloxane fluids against degradation in the presence of kaolin clay, without the use of potentially hazardous or corrosive amine compound additives. A further object of this invention is to obtain the above improvements without significantly affecting the properties of the silicone fluids, except for improved resistance to degradation induced by kaolin clay.